1. Field of the Invention
The present invention relates to an operational status testing apparatus and a method for an Ethernet-based automatic protection switching (APS) process, and more particularly, to an operational status testing apparatus and a method for an Ethernet-based APS process, in which an operational status testing function and a protection switching status maintaining function of an APS process stipulated by ITU-T recommendation G.8031 are made to complement each other and are improved.
This work was supported by the IT R&D program of MIC/IITA [2006-S-061-02, R&D on Router Technology for IPv6 based QoS Services and Host Mobility].
2. Description of the Related Art
Protection switching (PS) allows at least one reliable connection path to be formed between two nodes connected via a network and, when a failure occurs in the connection path, communication can be achieved by using a previously reserved protection connection path.
An Ethernet protection switching function is defined by ITU-T recommendations G.8031 and G.8032. Here, ITU-T recommendation G.8031 defines a protection switching method for an Ethernet point-to-point connection, and ITU-T recommendation G.8032 defines a protection switching method for an Ethernet ring connection. The present invention relates to a function for testing whether a protection switching function is performed normally between both nodes connected via an Ethernet regardless of a method for connecting both nodes connected via the Ethernet. However, since ITU-T recommendation G.8032 has not been recognized as an official recommendation yet, only Ethernet linear protection switching stipulated by ITU-T recommendation G.8031 will now be described.
ITU-T recommendation G.8031 stipulates a 1-phase APS process in a 1:1 or 1+1 configured linear connection network architecture. Nodes at both ends of a protection domain are connected to each other via two paths, which are called a working transmission path and a protection transmission path, respectively. The working transmission path is a path through which data is interchanged between both ends of the protection domain at normal times and the protection transmission path is a reserved path for the case where a failure occurs in the working transmission path. An APS process is used in nodes at both ends of the protection domain so as to interchange path status information and a protection switching command.
The APS process is very important when a function for managing a protection switching operation is performed. If the APS process is stopped or a malfunction occurs at either end of the protection domain, a transmission path between both ends of the protection domain may be intercepted.
In order to prevent this situation, ITU-T recommendation G.8031 defines a test command (hereinafter, referred to as an EXER request) to check whether another node's APS process is performed normally at both ends of the protection domain. In other words, two nodes are located at both ends of the protection domain and connected each other. One node transmits the EXER request to the other node if necessary, and the other node who has received the EXER request checks its own APS process. If it is checked whether the APS process is performed normally, the other node makes a previously defined response, thereby indicating the operational status of the other node's APS process.
ITU-T recommendation G.8031 which has been published in 2006 defines NR (No Request) or DNR (Do Not Revert) in response to the EXER request. However, since NR or DNR may be confused with a response that is normally received from another node, NR or DNR is being modified by defining a new response that is called RR (Reverse Request) so that RR can be distinguished from other responses.
However, such a modification conflicts with the operation of the conventional APS process because the priority of a response to the EXER request becomes high.
In the conventional APS process, the priority of a status or request of a node of APS process own (hereinafter, referred to as a local request) is compared with the priority of a status or request that is received from another node at a far end of the protection domain (hereinafter, referred to as a far end request) and whichever request has the higher priority is considered as a final request (hereinafter, referred to as a global request), as illustrated in FIG. 1.
For example, both ends of the protection domain are set in a non-revertive mode, and a failure occurs in the working transmission path, and the data transmission path is changed to the protection transmission path, and the failure in the working transmission path is being recovered. If the switched state is maintained, a DNR request is transmitted to another node at a far end of the protection domain, even though the working transmission path is being recovered. In this situation, if one node transmits the EXER request the other node at the far end of the protection domain, the other node checks its own APS process and sends a RR response. Then, the EXER request is revoked and the DNR request is returned, and the other node also revokes the RR response and must also send the DNR request.
However, as illustrated in FIG. 2 which relates to priorities of each request and status defined in ITU-T recommendation G.8031, since the priority of RR is higher than that of DNR, it is not possible that the RR response is revoked and returned to the DNR request.